AGE-INDEPENDENT CORRELATION OF OPTICALLY DETERMINED THORACIC KYPHOSIS WITH LUMBAR SPINE BONE MINERAL DENSITY

Abstract

The thoracic spine is susceptible to age-related increases in the sagittal curve, a process which is accentuated in osteoporosis. Previous studies have demonstrated an association between low vertebral bone mineral density (BMD) and accentuation of kyphosis. However, concerns of ionizing radiation associated with radiographic evaluation of osteoporotic fracture risks create a demand for alternative noninvasive detection methods. Back shape, and in particular the thoracic kyphosis, may act as a surrogate for bone density and complement methods of screening individuals for osteoporosis or monitoring progression. The aim of this prospective study is to establish the statistical association of mean lumbar spine BMD and the age-independent BMD Z-score with kyphosis, measured from noninvasive, rasterstereographic analysis of back shape. Back shape imaging of 42 females was performed following routine lumbar bone densitometry using dual energy X-ray absorptiometry. Kyphosis parameters derived from an optical back shape imaging system were correlated, using simple linear regression models, against mean lumbar BMD and BMD Z-scores. Moderate associations were noted between lumbar BMD and thoracic kyphosis (r=0.63 to 0.71, p<0.0001). The trend was still evident when correlating kyphosis against BMD Z-scores (r=0.57 to 0.68, p<0.0001). These data confirm earlier studies comparing radiographic indices of thoracic curvature with vertebral BMD, and suggest potential application of noninvasive back shape imaging to assist in the screening of individuals at risk of spinal osteoporosis, particularly in younger populations.